The debate between industry representatives and environmentalists over water quality standards for many of the state’s largest rivers should have quieted last year after lawmakers set a dissolved oxygen standard for these waterways. The new rule is already being challenged as too lenient although it has yet to be tested through a summer, the most critical time for fish survival. Instead of changing the standard so soon, lawmakers should give it a chance to work and be evaluated.

Dissolved oxygen consists of the gas bubbles that fish need to take in through their gills for survival. It comes from photosynthesis in plants in and along the river and from the river flow itself, when oxygen is mixed into the water. Nutrient pollution, such as phosphorus from a paper mill or sewage overflow from a treatment center, can reduce dissolved oxygen levels by sparking blooms of algae, which use up all of the river’s oxygen as they decompose. Cold water is better able to hold oxygen so problems arise in Maine only during the summer when water temperatures can climb into the 70s.

Federal law requires that rivers have enough dissolved oxygen to ensure the survival of native species. Sensitive juvenile trout and salmon in Maine can require up to 6 parts per million of dissolved oxygen.

For decades, the Maine Department of Environmental Protection had no standard for long-term average dissolved oxygen levels in many waterways, although it did set standards on some waterways on a case-by-case basis. Last year, the DEP decided to propose a statewide standard, although waterways with standards already in place were not covered by the new rules. This meant that the new rules would affect only the Androscoggin and St. Croix rivers, both of which have paper mills on them.

The department recommended that the level be set a 6.5 million parts per million at a water temperature of 24 degrees Celsius, which is about 75 degrees Fahrenheit. After much lobbying from the paper industry, the Legislature adopted the 6.5 ppm limit, but set the temperature at 22 degrees Celsius, about 72 degrees Fahrenheit. A body of water can sustain more pollution and still meet the dissolved oxygen standard at lower temperatures.

Due to a drafting error, the new law could not be approved by the Environmental Protection Agency. The DEP is back this year with a bill to correct the error. At the same time, a bill has been introduced to use the stricter 24-degree standard.

This is premature. According to Andrew Fisk, director of the DEP Bureau of Land and Water Quality, the standard already approved by lawmakers covers the range where 98 percent of fish growth takes place. A higher 24-degree standard would lead to only “marginal” improvements over what was passed last year.

The standard passed last year should be given a chance to work.